Shaft for use in nuclear radiation environment



July 30, 1963 H. GARTEN ETAL 3,099,141

SHAFT FOR USE IN NUCLEAR RADIATION ENVIRONMENT Filed Nov. so, 1961 P l Ill [lll Illl lll/ 'f Y' f 'Y fr Y Illl lll lill/[IIIA WMM/ MM United States Patent O 3,099,141 SHAFT FOR USE IN NUCLEAR RADIATHN ENVIBGNMENT Herbert Garten and Robert Herman Schaffer, Cincinnati,

Ohio, assignors to General Electric Company, a corporation of New York Filed Nov. 30, 1961, Ser. No. 156,189 S Claims. (Cl. 64-1) This invention relates to a torque-transmitting member, and, more particularly, to a shaft for use in a nuclear radiation environment wherein heat induced in the member by radiation is substantially proportional to the mass of the member.

Recent studies have proven that nuclear flight at subsonic, and possible supersonic speeds is feasible. These studies have primarily been concerned with two different avenues of approach for a nuclear powered aircraft jet engine, namely, an indirect cycle and direct cycle configuration. In an. indirect cycle nuclear .turbojet aircraft engine the nuclear radiation source, or reactor is placed off to one side of the engine and the conventional chemical combustion chamber heat source is replaced by a large radiator. The radiator is kept hot by a closed-loop heat transfer system in which a flu-id is circulated through the reactor and into the radiator and back to the reactor. On the other hand, in the direct cycle configuration the reactor replaces the normal chemical `fuel combustion chamber of the turbojet engine and the engine airiiow and the compressor power shaft pass through the reactor. Thus, a direct cycle nuclear turbojet engine may be described as an in-line engine, with the coupling shaft between the compressor section and the turbine section of the engine passing through the center of the reactor, or nuclear radiation source.

As in the conventional chemically fueled turbojet aircraft engine, the shaft must transmit both a torque load and an axial load. However, contrary to the situation in the conventional engine where a nuclear heat or radiation source is not present, heat is lgenerated in the shaft as it passes through the reactor, the amount of which is substantially proportional to the mass of the shaft. While cooling air may be directed against the shaft in any one of a number of known ways, this may not be enough to ofi-set the increased heating effect of the nuclear radiation. Thus, contrary to the normal application where there is no limitation against strengthening of the shaft by simply increasing its mass, or weight, in a direct cycle nuclear engine a heavier shaft will run hotter. This is unacceptable because of fthe fact that the metallic materials of which such shafts are usually constructed normally lose their strength with increasing temperature. While it would -appear that the shaft could be strengthened merely by increasing its diameter, for a nuclear turbojet applica-tion this will be undesirable since any increase in shaft diameter will be `accompanied by a significant increase in reactor overall diameter. This, in turn, affects reactor shielding requirements adversely, so that the net result is an intolerable overall weight increase. The problem, therefore, becomes one of providing, in a nuclear environment, a shaft capable of maximum torque, or power transmission, the shaft being of `minimum diameter and weight, since increasing weight becomes self-limiting in the shaft, it being clear that in any successful airborne application the total system weight is of critical importance.

Therefore, an object of this invention is to provide a shaft of minimum diameter and weight for use with a nuclear radiation source, which shaft has a configuration minimizing nuclear heat generation and temperature in the shaft, the shaft providing maximum power transmission.

'In one embodiment, the shaft of the present invention comprises a hollow, cylindrical member having a iin (or gldl Patented July 30, i963 fins) integral therewith, the tin being in the form of a helix having a predetermined angle and direction, the ratio of the total fin mass to the total mass of the member, excluding the iin, also having a predetermined value, wherein the fin acts as a load-transmitting member itself, thus pr-oviding maximum load carrying capability with minimum total shaft weight and heat generation in the nuclear radiation environment.

FIGURE l is a longitudinal view of the shaft, partially in cross section, in combination with a nuclear radiation source;

FlGURE 2 is a yview taken along line 2--2 of FIG- URE `l;

FEGURE 3 is a segment o-f a helical lin in cross section taken along line 3--3 in FIGURE 1 showing the relationship of the depth and pitch of the tin; and

FIGURES 4, 5, 6, 7, and 8 are 4graphical representations of -certain parameters governing the design of the invention.

Referring now more specifically to FIGURES l and 2, indicated generally by numeral il@ is a tubular member, or shaft. The tubular member, or shaft is preferably of onepiece construction and is adapted to transmit rotational force, or torque between a driving component and a driven component (not shown). For example, in aircraft applications the shaft may find use in a nuclear turbojet engine wherein in the usual manner one or more compressors are driven by one or more turbines downstream of the compressor. As seen in the drawing, the shaft extends through a nuclear radiation field, in this instance, a reactor. The shaft is a hollow, preferably cylindrical, seamless member, and includes a shell portion Ztl and a plurality of iin portions 5b. The shaft wall, or shell thickness tS is preferably relatively small so that the shaft, for a given diameter and length, can be more easily cooled.

As pointed out, when a metallic member, in particular, is used in la nuclear environment Iit will be subject to nuclear radiation such that heat is lgenerated in the member, in this case the shaft lili. The heat so generated will be substantially proportional to the mass of the metal in the member. While the mass MS of the shaft 10 has been significantly reduced by the descrioedV thin-walled configuration, it will be apparent that with a given power transmission requirement a certain degree of structural strength in the shaft will still be required. Thus, the problem, as stated, is to provide sufficient power, or load transmission capability (in the case of a turbojet engine, torque load and axial load) with minimum weight in the nuclear radiation environment. Since a heavier shaft will run hotter and since metallic materials, especially, lose their `strength with increasing temperature, the wall thickness fs cannot merely be increased.

As is well known, while a smooth shaft generally is most efficient in carrying a load, a finned shaftv of an equivalent tot-al mass will run cooler, thus raising the allowable stress in the shaft. However, the actual stress in commonly used finned shafts will be increased because the fins carry only an insignificant part of the load. This then raises the stress in the shell portion of the shaft as a result of the reduced masspthereof, since part of the original, or equivalent mass has been converted to tins. However, if the increase in the allowable stress exceeds this increase in actual stress, the use of such lins may be justified. But fins can only be justified in an airborne application if they do useful work, i.e., if they aid in power transmission. In other words, if lthe fins can be made to function as la `structural portion of the shaft and not merely as a means for cooling the shaft, they will justify their use. Thus, while it was known to provide a shaft with fins for the purpose of cooling, it was not, prior to the present invention, readily apparent that the addition of fins to a shaft, which would seem at best a grossly inefficient way of invangle of the ns is creasing shaft strength, could solve the problem of increasing the torque or load transmitting ability of a shaft in a nuclear enviroment, without unduly increasing shaft diameter or weight.

Therefore, with a fixed shaft `diameter and length, fixed flow rates and properties of the cooling uid utilized, if any, and a fixed internal heat generation rate for the nuclear radiation source through which the shaft must pass, the inventors have devised preferred embodiments of the shaft determined by such parameters as the shape of the iin, or fins, 3), the angle of the helix formed by each iin as it spirals internally of the shaft along the shaft length, the direction of the helix, the :total shaft mass Ms, and the total iin mass MF. The relationships yof these parameters are utilized to attain maximum shaft power transmission capability and minimum weight in a nuclear environment. Briefly, the inventors have `optimized the iin helix angle and the ydirection of the helix 'in order that the iin carries as much of the loads as possible, thus minimizing the effective stress on the shell. Also optimized is the thickness of the shell so that too small a thickness is avoided, since stresses would be too high, and too great a thickness is avoided, since with the high temperatures of a nuclear heating environment, an undue increase in the thickness would cause such a deeline in the material properties as would over-balance the reduction in stress and, although beefed-up, the shaft would actually be less safe. Moreover, the shape and chosen so as to minimize or eliminate the effects of manufacturing tolerance variations in the nuclear environment, i.e., uneven heating which may cause shaft bowing, or arcing.

In describing how the shaft is designed to achieve lthe desired load-carrying capability with any given shaft diameter in an application requiring minimum weight, par* ticular reference is made to FIGURES 4 through 8. FIG- URE 4 illustrates a parameter affecting the loadcarrying capability of the member 1G. In the graph, the torque load-carrying capacity is plotted as a function of the shaft weight for several values of the ratio of the total of n mass MF to the total shaft mass Ms. To understand the significance of the curves, first consider the curve Where the shaft is smooth, =i.e., there are no ns (MF/M520). In this instance the torque load-carrying capacity is low in the nuclear environment for either a light or heavy shaft, altho-ugh somewhat greater for some intermediate Weight. The reason for this is that an extremely lightweight shaft is is easily cooled because the shaft wall is relatively thin. However, depending on the extent of the thinness there may not be enough shell material to carry the torque load for a particular application so that the shaft thickness, and the Weight, may necessarily have to be increased. At rst, `cooling will still be reasonably effective and the material strength will `decline comparatively slowly. Thus, additional material increases the load-carrying capacity and the curve in FIG- URE 4 will rise. As the shaft thickness is increased still further in a nuclear radiation environment, however, the cooling becomes less effective and the shaft operating temperature rises rapidly. This ydrastically reduces the material strength the result being that the shaft is weakened Ifaster than the additional material can make up the strength, causing the load-carrying capacity to fall again. 'Dh-us, for a given application (or temperature margin, in a nuclear radiation environment) one particular shaft thickness will produce the strongest shaft. The curves in FIGURE 4 are therefore characterized by a downward concavity. If the shaft is then provided with fins, for the reasons'given above, the curves for different values at MF/MS will still be characterized by a `downward concavity.

Considering next the relationship between the curves, since, as stated above, the problem is one of obtaining the greatest load-carrying capacity in the peculiar en- -vironment of a nuclear radiation source, the effect on shaft design of the heat generation rise lbeing proportional to mass increase will be examined. FIGURE 5, as Well as IFIGURE 4, indicates that the iins can increase the ternperature margin (a corollary of load-carrying capacity in a nuclear radiation environment) significantly with predetermined increases in the MF/MS ratio within a certain range of values. Thus, by selecting an optimum value for the shaft weight, a maximum temperature margin may be obtained. In the example given for a shaft weight of 3 units, chosen as an optimum Ifor a smooth (unfinned) shaft, the best value of MF/MS is .5 since it provides the greatest temperature margin It will be noted that increasing the fin mass beyond a certain point will not raise the load-carrying capacity significantly, even when the shaft Weight is increased, since with too large a fin the resultant increase in shaft shell stress necessitates beeiing-up the shaft to the point where, in a nuclear radiation iel'd, the resultant temperature rise so weakens the material strength as to overcome the effect of the added weight. This, as pointed out, is not a problem in a non-nuclear environment. Also, as seen in the graph in FIGURE 5, the increase in MF/MS from .5 to 1.0 accomplishes something less than the increase from 0 to .5. This indicates that for very large values of the ratio MF/MS, the full cooling effectiveness will not be attained, and, further, stress concentrations may become a limiting factor. Therefore, optimization of the finned shaft load-carrying capability for a desired minimum weight may be accomplished by use of the graphs in FIG- URES 4 and 5. By choosing a desired torque load-carrying capacity (or temperature margin) and representing it as the ordinate of the graph, the abscissa may then represent the desired range of values for shaft weight. Curves for various ratios of t-he total fin mass to the total shell mass -MF/MS-can then be plotted. The first curve intersected by a horizontal line drawn at the desired torque load (or temperature margin) specifies the lightest shaft for the `given conditions. The inventors have determined that the preferred value for the ratio MF/MS will lbe greater than .2 but :less than 1.5 for aircraft nuclear turbojet engine applications.

It should be understood that the iin ratio just discussed is a mechanical rather than a thermal parameter, i.e., since the ratio is the total amount of fin material to the total amount of shell material, it deals only with the loadcarrying capacity of the fin member. On the other hand, the best thermal iin ratio, which is defined here as the ratio of the total surface area of the n and shell portion combined, to that of the surface area of a comparable smooth surfaced cylinder of equal diameter, obviously will 4depend somewhat upon the amount and properties of the cooling fluid utilized, if any, in the particular application. In a nuclear radiation environment, larger thermal fin ratio values will reduce shaft iinv temperature very effectively. However, the shell temperature will be reduced yonly slightly, so that the reduction in shell temperature is more than offset by an attendant increase in shell stress. The increase in thermal fin ratio virtually necessitates a simultaneous increase in MF/MS which causes the attendant increase in shell stress. Thus, with the present invention, where the ns are provided with a load or torque carrying capability, it has been found that the optimum thermal ratio, as defined, which results is preferably on the order of approximately two to one.

Refenring now to FIGURE 6 shown therein is one effect of differences in the value of the fin helix angle 0 on the shaft load-carrying capacity. It will be noted that for pure torque loads Ian tangle of appnoximlately 45 is best, although it is not critical. For a shaft which carries la combination of axial and torque loads, suc-h as in an aircraft tumbojet, the `curves in [the FIGURE 6 indicate that the .angle is optimum between 30 and 55. However, it was ldetermined that to avoid the effects of unbalance due to thermal bow of the shaft in the nuclear radiation environment, which causes one surface of the shaft to experience a greater temperature rise than the other, thus causing the shalt centerline to arc longitudinally, each lin should spiral at least one complete revolutio-n. Thus, the angle of the helix is also dependent on the relationship of the diameter to the length of the shaft. The optimum value of the angle was therefore determined to depend primarily on two parameters. One of these is the ratio of the diameter D times the axial load F to the torque load T, Ior D F/ T. For values of D XF/ T less than 3, the optimum value of 6 is between 30 and 55; tor values of DXF T greater than 3, the optimum value of 0 is from 0 to 30. This is shown graphically in FIGURE 7. However, the value of 0 must also be such as to insure that the relationship of the shaft diameter D to its length s permits each iin, `or helix to make approximately ione complete revolution. Thus, changes in D, in DXF T, will also aiect the relationship of D to s.

Further, the direction ot a fin, or helix in a shaft will be found to coincide gene-rally with :the direction of the maximum torque load. Tor maximum torque load-carrying capacity in the nuclear environment it has been found that, additionally, the direction of the helix should be such that the torque load tends to tighten the spiral, thus putting the tins in tension, and increasing the load-carrying capacity of the shaft.

Finally, the :graph in FIGURE 8 illustrates the rfact that the tin shape must also be taken into consideration when optimizing the sha-ft and in torque load-carrying capacity. In FIGURE". 3 the conguration of the llin is depicted in terms of the relationship of the height, or depth of the 1in d to the pitch of the helix p. With a lin ilank angle of approximately 15, or in the range `from 5 to 30, and a substantial llet approximately equal to the shell thickness at the base of the lin, to reduce stresses, the iin shape which combines the best heat transfer 0r cooling properties with mechanical strength tor load-carrying capabilities will have a configuration substantially as that show-n in FIGURE 3. In the embodiment shown the lin slenderness ratio for maximum load-carrying capacity is approm'rnately .3; but, in any event, in the range from .1 to '2.0. This ran-ge will also give the greatest in cooling effectiveness with a maximum strength and minimum weight in the nuclear environ-ment.

Thus, the inventors have provided a new land useful torque and axial load-transmitting member `ior use in a nuclear radiation iield wherein the heat Vgenerated in the member, as a result of nuclear heating, will be substantially proportional to the mass thereof. The member has a hollow shell yand helical ns integral with either the outer surface of the shell, or lthe inner surface of fthe shell, or both. Further, the helix direction is to be determined by vthe direction of the torque load, and the preferred value of .the ratio MF/MS is greater than .2. but less than 1.5, the preferred angle of the helix is greater than 30 but less than 55, the value of the ratio (as lmeasured perpendicul-uar to the lin helix angle) is preferably greater .than .1, but less than 2.0, with the lin proportioned in la manner so that its flank angle is greater than 5 but lless than 30, and the thermal iin ratio is approximately 2 to l, in order that the shaft will provide maximum power transmission with minimum overall weight in the nuclear radiation lield.

What we claim and desire to secure by Letters Patent 1. A load transmitting member -for use in a nuclear radiation environment wherein the temperature rise in 6 the member is substantially proportional to its mass, said member comprising:

a hollow, cylindrical shell portion, said shell portion transmitting a part of ysaid load and having a total mass MS;

a lin integral with .a helix extending the length of the having a total mass MF,

wherein the ratio of `the iin mass to the shell mass- M F/M S-is greater than .2 but less than 1.5,

so as to enable said lin to transmit the remaining part of said load at la minimum total weight lof said member in said nuclear radiation environment.

2. A load transmitting member tor use in a nuclear radiation environment wherein the temperature rise in the member is substantially proportional to its mass, said member comprising:

la hollow, cylindrical shell portion, said shell portion transmitting a part of said load;

a -tin integral with said shell portion, said iin comprising a helix extending the length of the shell portion rand having a height d and a pitch p,

wherein the ratio of the liin height to the tin pitchd/ p-is greater than .1 but less than 2.0,

so 4as to enable said lin to transmit the remaining part of lsaid load at a minimum total weight ot said member in said nuclear radiation environment.

3. A load transmitting member for use in a nuclear radiation environment wherein the temperature rise in the member is substantially proportional to its mass, said member comp-rising:

la hollow cylindrical shell portion, said shell portion transmitting a part of said loading and having a total mass MS,

la fin integral with said shell a helix extending the length of the shell portion having `a height d and a pitch p, wherein the ratio lof the lin height to the iin pitchd/p-is greater than .l Ibutless than 2.0,

land wherein the ratio off the lin mass to the shell mass- MF/MS--is greater than .2. but less than 1.5,

so as to enable said lin to transmit the remaining part of said load at a minimum total weight of said member in said nuclear radiation environment.

4. A torque load transmitting member tor use in a nuclear radiation environment wherein `the temperature rise in the member is substantially proportional to its mass, said member comprising:

a hollow, cylindrical shell portion, said shell portion transmitting a part of said load;

a fin integral with said shell portion, said lin comprising a helix extending the length of the shell portion and having a height d and a pitch p land an angle 0;

wherein lthe natio of the tin height to the iin pitchd/p-is greater than .l but less than 2.0,

and wherein the direction fof the helix is such that twisting in said member due to the torque load will tend to tighten said -an-gle 0 of the helix,

so las to enable said tin to transmit the remaining part of said load lat a minimum total weight of said member in said nuclear radiation environment.

5. A torque and axial load transmitting member for use in a nuclear radiation environment wherein temperature rise in the member is substantially proportional to its mass, said `member comprising:

a hollow, cylindrical shell portion, said shell portion transmitting a part of the axial load F and the torque load T, said shell portion having a ldiameter D;

a tin integral with said shell portion, said iin comprising a helix extending the length of the shell portion;

wherein the angle of said helix is such that when the value of the ratio DXF/T is less than 3, the optimum helix angle will be -greater than 30, but less than 55, and 'when the yvalue of the ratio is greater than 3, the optimum helix angle will be less than 30,

said shell portion, said iin comprising shell portion and portion, sai-d fin comprising and so as to enable said iin to transmit the remainder of said loads F and T at a total minimum weight of said member in said nuclear radiation environment.

6. A torque and axial load transmitting member for use in a nuclear radiation environment wherein temperature rise in the member is substantially proportional to its mass, said member comprising:

a hollow, cylindrical shell portion, said shell portion transmitting a part of the axial load F and the torque load T, said shell portion having a diameter D and a mass MS;

a iin integral with said shell portion, said iin comprising a helix extending the length of the shell portion and having a -mass MF;

wherein the angle of said helix is such that when the value of the ratio D XF T is less than 3, the optimum helix angle will be greater than 30", but less than 55 and when the value of the ratio is greater than 3, the optimum helix angle will be less than 30,

and wherein the ratio of the `iin mass to the shell mass-MF/MS--is greater than .2 but less than 1.5,

so as to enable said lin to transmit the remainder of said loads F and T to a total minimum weight of said member in said nuclear radiation environment.

7. A torque and axial load transmitting member for use in a nuclear radiation environment wherein temperature rise in the member is substantially proportional to its mass, said member comprising: e

a hollow, cylindrical shell portion, said shell portion transmitting a part of the axial load F .and the torque load T, said shell portion having a diameter D;

a iin integral with said shell portion, said iin comprising a helix extendingr the length s of the shell portion and having an angle wherein the angle 9 of said helix is such that said iin makes at least one complete revolution of said cylindrical shell portion along said length s, and wherein the angle 0 of said helix is such that when the value of the ratio DXF/ T is less than 3, the optimum helix angle will be greater than 30, but less than 55, and when the value of the ratio is greater than 3, the optimum helix will be less than 30, so as to enable said n to transmit the remainder of said loads F and T at a minimum total weight of said member I1n said nuclear radiaiton environment.

8. A torque and axial load transmitting member 'for' use in a nuclear radiation environment wherein temperature rise in the member is substantially proportional to its mass, said member comprising:

a hollow, cyl-indrical shell portion, said shell portion transmitting a part of the axial load F and the torque load T, said shell portion having a diameter D;

a iin integral with said shell portion, said fin compris-- ing a helix extending the length s of the shell portion and having a height d and a pitch p;

wherein the ratio of the iin height to the tin pitchd/p-is greater than .1 and less than 2.0,

and wherein the ratio of the total surface area of the iin and shell portion combined to that of the surface area of an unfinned load transmitting member of equal diameter D, is approximately 2,

so as to enable said 1in to transmit the remaining part of said loads F and T at a minimum total weightv of said member in said nuclear radiation environment.

No references cited. 

1. A LOAD TRANSMITTING MEMBER FOR USE IN A NUCLEAR RADIATION ENVIRONMENT WHEREIN THE TEMPERATURE RISE IN THE MEMBER IS SUBSTANTIALLY PROPORTIONAL TO ITS MASS, SAID MEMBER COMPRISING: A HOLLOW, CYLINDRICAL SHELL PORTION, SAID SHELL PORTION TRANSMITTING A PART OF SAID LOAD AND HAVING A TOTAL MASS MS; A FIN INTEGRAL WITH SAID SHELL PORTION, SAID FIN COMPRISING A HELIX EXTENDING THE LENGTH OF THE SHELL PORTION AND HAVING A TOTAL MASS MF, WHEREIN THE RATIO OF THE FIN MASS TO THE SHELL MASSMF/MS-IS GREATER THAN.2 BUT LESS THAN 1.5, SO AS TO ENABLE SAID FIN TO TRANSMIT THE REMAINING PART OF SAID LOAD AT A MINIMUM TOTAL WEIGHT OF SAID MEMBER IN SAID NUCLEAR RADIATION ENVIRONMENT. 